ADS not showing @ ad_showthread_firstpost_start

[ddo36]

how come the ads by google doesnt show on the first post?
the ads are created a few days back already. they're not new.
on the early days, ads are showing, but know, it's not showing anymore. no matter what ads i place. why?

This is the code i placed at "ad_showthread_firstpost_start "

<if condition="$bbuserinfo['usergroupid'] == 1">
<div style="float:right; width:300px; height:250px; margin-left:10px">

<script type="text/javascript"><!--
google_ad_client = "pub-3468565034734280";
/* 300x250, created 5/29/09 */
google_ad_slot = "4032835295";
google_ad_width = 300;
google_ad_height = 250;
//-->
</script>
<script type="text/javascript"
src="http://pagead2.googlesyndication.com/pagead/show_ads.js">
</script>

</div>
</if>